1. Technical Field
The present invention relates generally to creating and managing wireless networks.
2. Background of the Related Art
An access point is a device that acts as a central point between a wireless and a wired network. When multiple access points are installed within close proximity, installers must choose proper radio channels to minimize inter-access point interference, which can degrade the performance of a wireless LAN. Access point devices that include automatic channel selection are known in the art. The access point senses the presence of other access points and attempts to adjust to a quieter channel.
Wireless LAN technologies operate according to a family of IEEE specifications known as 802.11. In particular, the basic 802.11 standard specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. 802.11a is an extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5 GHz band. 802.11b is an extension to 802.11 that applies to wireless LANs and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. In 802.11b, the frequency band is 2.4 GHz to 2.4835 GHz. The first channel (Channel 1) is placed at center frequency 2.412 GHz, and subsequent channels are at 5 MHz multiple from the first channel (except channel 14, which is not a multiple of 5 MHz). This arrangement gives a total of 14 channels. In the United States, only channels 1 through 11 are allowed by the FCC. Channel 10 is allowed by all (world) regulatory authorities, and most manufacturers use this channel as the access point default channel. In the United States, the 802.11a channels are channels: 52, 56, 60, 64, 149, 153, 157, 161, and 165. These channels are separated by at least 20 MHz. This is also true for 802.11a channels in other parts of the world.
There are two possible modes of operation for an access point: 802.11b/g channel mode, and 802.11a channel mode. The signal interferences in these 802.11 modes are much different from each other, primarily because of differences in channel spacing and radar signal presence or lack thereof. In 802.11a mode, the channels are spaced far apart from each other; therefore, there is little co-channel interference. As noted above, the spacing between two adjacent channels is 20 MHz. FIG. 1 shows a transmit spectrum mask where a transmit signal's frequency beyond 22 MHz off center is −50 dBr (meaning that its power is reduced by 100,000). Because of this characteristic, finding a radar free channel that has a least amount of intra-channel interference is a problem in 802.11a. Note, however, that 802.11a avoids interference from cordless phones and microwaves because these devices operate in the 2.4 GHz frequency range. In 802.11b mode, as also illustrated in FIG. 1, the channels are only 5 Mhz apart; as a result, there is a strong possibility of adjacent channel interference. To achieve non-overlapping channels in 802.11b, channels 1, 6 and 11 are often used to provide the necessary 20 MHz separation.
In practice, however, access points may be configured to operate on any channel. It would be desirable to provide automatic channel selection algorithms that are not dependent on given assumptions, such as that all access points belong to certain channels, or that otherwise takes into account that all channels are likely to be used by neighboring access points.
The present invention addresses this need in the art.